1. Technical Field
Illustrative embodiments described in this patent specification generally relate to an image forming apparatus such as a copier, a printer, a facsimile machine, and a multifunction device having two or more of copying, printing, and facsimile functions, and more particularly to a drive transmission mechanism that transmits a driving force from a rotational driving source to members to be rotated such as a photoconductor, a developing sleeve, and a developer agitation screw included in the image forming apparatus.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
There is increasing demand for forming higher-quality full-color images using full-color image forming apparatuses, and various image forming methods have been employed in the full-color image forming apparatuses in recent years to meet such a demand. One example of a full-color image forming apparatus includes a single photoconductor, and multiple developing devices corresponding to respective colors of toner are provided around the photoconductor. Toner images of the respective colors are attached to the photoconductor using the multiple developing devices to form a full-color toner image on the photoconductor. The full-color toner image thus formed is then transferred onto a recording medium such as a sheet of paper to form a full-color image on the sheet.
Another example of a full-color image forming apparatus employs a tandem system, in which multiple photoconductors corresponding to respective colors of toner and multiple developing devices respectively corresponding to the multiple photoconductors are provided. Toner images of the respective colors formed on the multiple photoconductors are sequentially transferred onto a sheet and superimposed one atop the other to form a full-color toner image on the sheet.
Compared to the tandem-type full-color image forming apparatus, the full-color image forming apparatus having the single photoconductor has certain advantages, e.g., the size and production costs can be reduced due to the reduced number of photoconductors used for full-color image formation. However, because multiple sequences of image formation are performed using only the single photoconductor, it is difficult to achieve full-color image formation at higher-speed. By contrast, although the size and production costs of the tandem-type full-color image forming apparatus are not easily reduced, the tandem-type full-color image forming apparatus has an advantage in that higher-speed full-color image formation can be achieved. Increasing demand for full-color image formation as fast as monochrome image formation has made the tandem-type full-color image forming apparatus common in recent years.
The tandem-type full-color image forming apparatus employs either an intermediate transfer system or a direct transfer system. In the intermediate transfer system, the image forming apparatus mainly includes the multiple photoconductors corresponding to the number of colors of toner necessary for full-color image formation and an intermediate transfer body such as an intermediate transfer belt. Toner images respectively formed on the multiple photoconductors are primarily transferred onto the intermediate transfer belt by a primary transfer unit, so that toner images are sequentially superimposed one atop the other to form a full-color toner image on the intermediate transfer belt. The full-color toner image thus formed is then secondarily transferred onto a sheet from the intermediate transfer belt by a secondary transfer unit so that a full-color image is formed on the sheet. By contrast, in the direct transfer system, the image forming apparatus mainly includes the multiple photoconductors and a conveyance belt. Toner images respectively formed on the multiple photoconductors are directly transferred onto a sheet conveyed by the conveyance belt through a conveyance path so that the toner images are sequentially superimposed one atop the other to form a full-color image on the sheet.
Compared to the intermediate transfer system, the number of components and production costs can be reduced due to the absence of the intermediate transfer body in the direct transfer system. However, because the toner images formed on the photoconductors are directly transferred onto the sheet in the direct transfer system, the position of each of the toner images can shift upon transfer from the photoconductors onto the sheet when the position of the sheet is inadvertently changed for some reasons, a phenomenon known as color shift. By contrast, although the number of components and production costs are increased, the position at which to secondarily transfer the full-color toner image from the intermediate transfer belt onto the sheet can be set with less limitation in the intermediate transfer system. Accordingly, the degree of freedom to design the image forming apparatus is increased in the intermediate transfer system. Further, even when the position of the sheet is inadvertently changed for some reasons, the full-color toner image is already formed on the intermediate transfer belt so that color shift can be prevented.
In any type of full-color image forming apparatuses, a variety of different members to be rotated by a rotational driving force (hereinafter referred to as rotary members), such as the photoconductors, developing sleeves, and developer agitation screws are provided therein. In general, the rotary members are detachably attachable to the image forming apparatuses for maintenance or replacement, and a drive transmission mechanism is used to transmit the rotational driving force to the rotary member to rotate the rotary member. The drive transmission mechanism mainly includes driven members provided to the rotary members and rotational driving members detachably attachable to the driven members that are coupled to the driven members.
In such an image forming apparatus, image deterioration caused by image shift generally called banding (jitter) is a problem, and it is known that vibration generated between the rotational driving member and the driven member coupled to each other causes such banding. Therefore, generation of vibration needs to be prevented in order to satisfy the increasing demand for higher-quality images.
One of main causes of vibration is a shift between the center of rotation of the rotational driving member and the center of rotation of the driven member upon coupling of the rotational driving member and the driven member. For example, referring the developing sleeve as representative of the rotary member, the developing sleeve inevitably has production tolerances and installation tolerances. Consequently, it is very difficult to accurately position the driven member provided to the rotary shaft of the developing sleeve relative to the rotational driving member provided to the drive shaft. Further, each of the driven member and the rotational driving member has a protrusion so that a lateral surface of the protrusion of the driven member contacts with a lateral surface of the protrusion of the rotational driving member to couple the driven member and the rotational driving member to each other. However, because the protrusions also inevitably have production tolerances and installation tolerances, the center of rotation of the rotational driving member is shifted from the center of rotation of the driven member upon coupling of the rotational driving member and the driven member.
When the center of rotation of the rotational driving member is shifted from the center of rotation of the driven member upon coupling of the rotational driving member and the driven member, the protrusions respectively provided to the rotational driving member and the driven member repeatedly contact to and separate from each other while the rotational driving member and the driven member revolve once. Contact and separation between the protrusions cause impact, and the impact is transmitted to the components and a main body of the image forming apparatus, resulting in vibration causing banding and so forth. Consequently, the quality of full-color images formed by the image forming apparatus is degraded.
Various techniques have been proposed to reduce vibration causing banding in order to prevent deterioration in image quality. For example, an elastic body is twisted around one of protrusions respectively provided to the rotational driving member and the driven member to reduce vibration occurred upon coupling of the rotational driving member and the driven member. However, because the protrusion provided to one of the rotational driving member and the driven member is itself an elastic body, the elastic body may be deformed by collision, and the driven member and the rotational driving member are coupled to each other with the deformed elastic body. As a result, not only occurrence of vibration cannot be prevented, but also additional vibration may occur.
In another approach, a spring-like pick is provided for coupling the driven member and the rotational driving member in order to reduce occurrence of vibration. However, a hinged portion of the pick always receives the rotational driving force, thereby possibly causing a decrease in durability due to a load repeatedly applied to the pick when the rotational driving force is applied to the coupling, application of the rotational driving force to the coupling is stopped, and the coupling is released.
In yet another approach, coupling members are provided in the middle of a drive transmission path through which the rotational driving force is transmitted, and an elastic body is directly provided to a connection section where the coupling members are coupled to each other so that occurrence of vibration is reduced. However, attachment and detachment of the coupling members are very difficult in the above-described configuration. Consequently, employment of the above-described configuration is not appropriate for rotary members such as the photoconductor and the developing sleeve, which are designed to be detachably attachable to the image forming apparatus.